Contamination is “the presence of elevated concentrations of substances in the environment above the natural background level for the area and for the organism” (Sciortino and Ravikumar 1999). Contaminants (or chemical pollutants) represent a significant threat to the environment and marine mammal populations. The amount of synthetic chemicals continually introduced to the environment and the ways they may interact with each other.
Environmental contaminants include heavy metals (such as cadmium, lead and mercury), polycyclic aromatic hydrocarbons (PAHs), which are by-product of incomplete combustion or organic matter like oil and coal and persistent organic pollutants (POPs). POPs comprise polychlorinated biphenyls (PCBs), pesticides (including insecticides), as well as emerging pollutants like brominated flame retardants. The latter are very little metabolised and thus only slowly eliminated. These contaminants are resistant to environmental degradation and remain in the environment years after their release.
Environmental contaminants are highly fat-soluble and have the capacity to concentrate and accumulate as they make their way up the food chain – their concentration increases from one predator level to the higher level.
Among the different ways of toxicity, POPs and heavy metals are endocrine disruptors: they interfere with and disrupt the endocrine (hormonal) system. Environmental contaminants disturb the immune system (for example by increasing susceptibility to disease and decreasing resilience), the reproductive system and the central nervous systems (for example by affecting the development and the orientation for example).
Despite regulations and mitigation measures to reduce PCB pollution, PCBs continues to severely impact marine mammals. Data show a correlation between present reproductive failure in European harbour porpoise, killer whale and bottlenose dolphin populations and PCBs burdens (e.g., Murphy et al. 2015, Jepson and Law 2016, Jepson et al. 2016).
Environmental contaminants also transfer over long distances from their sources in industrialised regions to remote, usually non-industrialised regions, such as the Arctic. There, the high/fat soluble contaminants concentrate as they make their way up the high-fat Arctic food chains, causing negative impacts for those who subsist on these resources. Northern indigenous and local communities greatly rely on the sea and its resources for subsistence. However, even the remoteness and absence of local pollution sources do not guarantee the safety of Arctic wildlife populations and therefore the well-being of communities reliant on subsistence harvests. These communities remain vulnerable to the potential detrimental effects associated with these pollutants (Arctic Monitoring and Assessment Programme (AMAP) 2018).
Polar bears are also negatively impacted by environmental pollutants through eating contaminated meat. Polar bears in Svalbard show decreased levels in vitamin A and antibodies, and 1.5% of sampled females have partially-developed male sexual organs – pseudohermaphrodites (Wiig et al. 1998). East Greenland polar bears exhibit reduced bone density (osteoporosis) and size reduction in sexual and reproductive organs (Sonne et al. 2012). Both are believed to be the result of high concentrations of long-range environmental contaminants. Polar bears continue to exhibit levels of mercury that put them at risk (AMAP 2018). Combined with the effects of climate change for the species, the exposure to endocrine disruptors puts polar bears at risk of population declines (ibid.). Wildlife are exposed to a diverse and interlinked series of natural and anthropogenic stressors that may act cumulatively to impact wildlife health.
Chemicals are an integrated part of everyday life with over 100,000 different substances in use, and new ones are constantly emerging. There are hardly any industry where chemical substances are not in use and there is no single economic sector where chemicals do not play an important role. Therefore, their sound management is essential (see e.g., policy-relevant recommendations from AMAP 2018).
References
Arctic Monitoring and Assessment Programme (AMAP). (2018). AMAP Assessment 2018: Biological Effects of Contaminants on Arctic Wildlife and Fish. Available at https://www.amap.no/documents/doc/amap-assessment-2018-biological-effects-of-contaminants-on-arctic-wildlife-and-fish/1663
Jepson, P.D., Deaville, R., Barber, J.L et al. (2016). PCB pollution continues to impact populations of orcas and other dolphins in European waters. Scientific Reports, 6, 18573. https://doi.org/10.1038/srep18573p
Jepson, P.D. and Law, R.J. (2016). Persistent pollutants, persistent threats. Science, 352(6292), 1388-1389. https://doi.org/10.1126/science.aaf9075
Murphy, S., Barber, J.L., Learmonth J.A. et al. (2015). Reproductive Failure in UK Harbour Porpoises Phocoena phocoena: Legacy of Pollutant Exposure? PLoS ONE, 10(7), e0131085. https://doi.org/10.1371/journal.pone.0131085
Sciortiono, J.A. and Ravikumar, R. (eds.). (1999). Chapter 1: Potential pollutants, their sources and their impacts. In Fishery Harbour Manual on the Prevention of Pollution – Bay of Bengal Programme. BOBP For Fisheries Management. BOBP/MAG/22. Available at http://www.fao.org/3/x5624e/x5624e04.htm#1.1
Sonne, C., Letcher, R.J., Bechshøft, T.Ø. et al. (2012). Two decades of biomonitoring polar bear health in Greenland: a review. Acta Veterinaria Scandinavia, 54, S15. https://doi.org/10.1186/1751-0147-54-S1-S15
Wiig, Ø., Derocher, A.E., Cronin, M.M. and Skaare, J.U. (1998). Female pseudohermaphrodite polar bears at Svalbard. Journal of Wildlife Disease, 34(4), 792-796. https://doi.org/10.7589/0090-3558-34.4.792